Although thiodiglycol is already mentioned in some of our own earlier literature references (for example, German Patent No. 887,119 and DAS No. 1,031,512) as a possible starting component for the production of polycarbonates by conventional processes, repetition of the corresponding working procedures has shown that it is not possible in this way to obtain polycarbonates based on thiodiglycol (cf. Comparison Examples 1 to 4). Any attempt to transesterify thiodiglycol with dicarbonates, such as diphenyl carbonates, results in vigorous evolution of CO.sub.2, and produces condensation products of very low molecular weight having practically no carbonate groups. On the other hand, direct condensation with phosgene or bischloroformic acid esters is accompanied by decomposition of the reaction mixture into products of high chlorine content, the elimination of water and mustard-gas-like compounds. The conclusion to be drawn from the results of these tests is that thiodiglycol polycarbonates are substantially unstable.